Multiaxial Modular Tibia Stems

FIELD The present disclosure is related to total ankle replacement.

BACKGROUND

Tibia stem components help engage implants where limited bone is available for total ankle arthroplasty. Pistoning or loosening of the implant can present as a long term complication. Thus, improved tibia stem components that can better engage with the tibia bone and improve immediate implant stability and reduce implant migration over time are desired.

SUMMARY

Disclosed herein are implants designed to engage cancellous, and possibly cortical, tibia bone to improve immediate implant stability and reduce implant migration over long term. Disclosed is an ankle prosthesis comprising: a tibia stem component comprising a leading end, a trailing end, and a longitudinal axis defined therethrough; and a tibia tray component configured to be attached to a prosthetic joint articulating surface, wherein the tibia tray component extends from the trailing end of the tibia stem component, wherein the tibia stem component is sized and configured to be disposed in an intramedullary canal formed in a tibia, wherein the tibia stem component comprises: one or more retractable members configured to be controllably movable from a retracted position and be extended outward and away from the longitudinal axis, wherein in the retracted position, the one or more retractable members are contained substantially within the tibia stem component and do not extend outward, wherein when the tibia stem component is disposed in the intramedullary canal and the one or more retractable members are extended outward, the one or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem within the intramedullary canal. Also provided is an ankle prosthesis, comprising: a tibia stem component comprising a leading end, a trailing end, and a longitudinal axis defined therethrough; and a tibia tray component configured to be attached to a prosthetic joint articulating surface, wherein the tibia tray component extends from the trailing end of the tibia stem component, wherein the tibia stem component is sized and configured to be disposed in an intramedullary canal formed in a tibia, wherein the tibia stem component is divided into two or more retractable members by longitudinal slits, extending from the leading end of the tibia stem component and partially toward the trailing end, formed in the tibia stem, whereby each of the two or more retractable members comprise a proximal end and a distal end, wherein their proximal ends are joined at the trailing end of the tibia stem component and their distal ends are freely moveable, wherein the two or more retractable members are configured to be controllably movable from a retracted position and be extended outward and away from the longitudinal axis, wherein in the retracted position, the two or more retractable members are parallel to the longitudinal axis and do not extend outward, wherein when the tibia stem component is disposed in the intramedullary canal and the two or more retractable members are extended outward, the two or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem within the intramedullary canal. Also provided is an ankle prosthesis, comprising: a tibia stem component comprising a leading end, a trailing end, and a longitudinal axis defined therethrough; and a tibia tray component comprising a surface defining a reference plane, wherein the tibia stem component and the tibia tray component are modular and the tibia tray component and the trailing end of the tibia stem component are configured to form a joint wherein the tibia stem component's relative angle with respect to the reference plane can be adjusted so that the longitudinal axis forms an angle θ with an orthogonal of the reference plane, wherein the angle can be between 0 degrees up to and including 40 degrees, wherein the tibia stem component is sized and configured to be disposed in an intramedullary canal formed in a tibia, wherein the tibia stem component comprises: two or more retractable members configured to be controllably movable from a retracted position and be extended outward and away from the longitudinal axis, wherein in the retracted position, the one or more retractable members are contained substantially within the tibia stem component, and wherein when the tibia stem component is disposed in the intramedullary canal and the two or more retractable members are extended outward, the one or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem within the intramedullary canal.

BRIEF DESCRIPTION OF DRAWINGS

The features of the embodiments described herein will be more fully disclosed in the following detailed description, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts. All drawings are schematic and are not intended to show actual dimensions or proportions. FIGS. 1 A- 1 L are illustrations of a prosthesis according to an embodiment of the present disclosure. FIGS. 2 A- 2 F are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 3 A- 3 J are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 4 A- 4 G are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 5 A- 5 F are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 6 A- 6 G are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 7 A- 7 G are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 8 A- 8 G are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 9 A- 9 C are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 9 D- 9 F are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 10 A- 10 C are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 10 D- 10 H are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 11 A- 11 F are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 12 A- 12 H are illustrations of a prosthesis according to another embodiment of the present disclosure. FIGS. 13 A- 13 B are illustrations of a prosthesis according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. The methods, systems, and structures described for the ankle herein may be adapted to other applications in arthroplasty, including but not limited to the knee, shoulder, hip, elbow, and other joints. Referring to FIGS. 1 A- 7 E , an ankle prosthesis 100 A, 100 B, 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, 100 I, 100 J is disclosed. The ankle prosthesis comprises: a tibia stem component 110 A, 110 B, 110 C, 110 D, 110 E, 110 F, 110 G, 110 H, 110 I, 110 J; and a tibia tray component 120 A, 120 B, 120 C, 120 E, 120 F, 120 G, 120 H, 120 I, 120 J configured to be attached to a prosthetic joint articulating surface. The tibia stem component comprises a leading end 111 A, 111 B, 111 C, 111 D, 111 E, 111 F, 111 G, 111 H, 111 I, 111 J a trailing end 112 A, 112 B, 112 C, 112 D, 112 E, 112 F, 112 G, 112 H, 112 I, 112 J and a longitudinal axis L defined therethrough. The tibia tray component extends from the trailing end of the tibia stem component. The tibia stem component is sized and configured to be disposed in an intramedullary canal formed in a tibia. The tibia stem component comprises one or more retractable members 130 A, 130 B, 130 C, 130 D, 130 E, 130 F, 130 G, 130 H, 130 I, 130 J configured to be controllably movable from a retracted position and extended outward and away from the tibia stem component. In the retracted position, the one or more retractable members 130 A, . . . 130 J are contained substantially within the silhouette of the tibia stem component and do not extend outward. Substantially within the silhouette of the tibial stem means that a small portion (no more than about 0.5 mm) of the distal ends of the one or more retractable members can, in some embodiments, protrude out beyond the silhouette of the tibia stem. In use, after the tibia stem component is disposed in the intramedullary canal of a tibia, the one or more retractable members are moved from their retracted position outward and away from the longitudinal axis L so that the one or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem within the intramedullary canal. In some preferred embodiments, the tibia stem component comprises two or more retractable members 130 A, 130 B, 130 C, 130 D, 130 E, 130 F, 130 G, 130 H, 130 I, 130 J. In many situations, having two or more retractable members can provide anchoring configurations that are more symmetrical. The symmetry involved here can be planar symmetry or radial symmetry with respect to the longitudinal axis L of the tibia stem component. Retraction of the retractable members 130 A, 130 B, 130 C, 130 D, 130 E, 130 F, 130 G, 130 H, 130 I, 130 J allows for in-situ adjustment, repositioning, and patient removal of the tibia stem component as necessary. In some embodiments of the prosthesis 100 A, 100 B, 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, 100 I, 100 J, the tibia tray comprises a channel 122 A, 122 B, 122 C, 122 D, 122 E, 122 F, 122 G, 122 H, 122 I, 122 J, extending between a pair of opposed rails 124 A, 124 B, 124 C, 124 D, 124 E, 124 F, 124 G, 124 H, 124 I, 124 J, for receiving the prosthetic joint surface. In some embodiments of the prosthesis 100 A, 100 B, 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, 100 I, 100 J, the channel in the tibia tray extends in an anterior-posterior direction, medial-lateral direction, or in an oblique direction. In some embodiments of the prosthesis 100 A, 100 B, 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, 100 I, 100 J, the one or more retractable members 130 A, 130 B, 130 C, 130 D, 130 E, 130 F, 130 G, 130 H, 130 I, 130 J extend away from the longitudinal axis L of the tibia stem component when moving from their retracted positions outward and away from the longitudinal axis L. In some embodiments of the prosthesis 100 A, 100 B, 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, 100 I, 100 J, the tibia stem comprises an elongated generally cylindrical shell defining an internal cavity 115 A, 115 B, 115 C, 115 D, 115 E, 115 F, 115 G, 115 H, 115 I, 115 J, that is open at the trailing end. An opening 116 A, 116 B, 116 C, 116 D, 116 E, 116 F, 116 G, 116 H, 116 I, 116 J is provided in the generally cylindrical shell of the tibia stem component for each of the one or more retractable members. The one or more retractable members extend outward through the opening in the cylindrical shell from the retracted position. Although, the shape of the shell forming the tibia stem component is referred to as being generally cylindrical, the scope of the present disclosure encompasses a variety of shapes for the shell other than those having circular or oval cross-section. The term “generally cylindrical” as used herein is intended to encompass a structure for the shell that can have a variety of other cross-sectional shape such as polygons (i.e., a triangle, a quadrilateral, a pentagon, a hexagon, a heptagon, an octagon, etc.). Additionally, the term “generally cylindrical” as used herein is intended to encompass structures that may not have a continuous solid shell such as the shell forming the tibia stem components in the prosthesis embodiments 200 A and 200 B shown in FIGS. 10 A and 11 A , respectively. The tibial stems in prosthesis embodiments 200 A and 200 B do not have solid cylindrical structures but they do have generally cylindrical shapes. In some embodiments of the prosthesis, the tibia stem further comprises a linear actuator 117 A, 117 B, 117 C, 117 D, 117 E, 117 F, 117 G, 117 H, 117 I, 117 J, provided within the internal cavity. The linear actuator is configured to be movable within the internal cavity along the longitudinal axis L. Each of the one or more retractable members have a distal end 131 A, 131 B, 131 C, 131 D, 131 E, 131 F, 131 G, 131 H, 131 I, 131 J and a proximal end 132 A, 132 B, 132 C, 132 D, 132 E, 132 F, 132 G, 132 H, 132 I, 132 J. The proximal end is attached to the linear actuator and the distal end is a free end that is movable through the respective opening 116 A, 116 B, 116 C, 116 D, 116 E, 116 F, 116 G, 116 H, 116 I, 116 J provided in the cylindrical shell of the tibia stem to engage the intramedullary canal's surrounding bone when the prosthesis is installed inside the intramedullary canal of a tibia. The movement of the one or more retractable members 130 A, . . . 130 J from the retracted position to being extended outward and away from the tibial stem component is controllably achieved by moving the linear actuator 117 A, . . . 117 J within the internal cavity 115 A, . . . 115 J. The movement of the linear actuator can be either toward the leading end 111 A, . . . 111 J or toward the trailing end 112 A, . . . 112 J in the axial direction along the longitudinal axis L. The controlled axial movement of the linear actuator can be enabled in a variety of ways. In the disclosed exemplary embodiments of the prosthesis 100 A, 100 B, 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, 100 I, 100 J, the axial movement of the linear actuator 117 A, . . . 117 J is achieved by a threaded action. For example, in the prosthesis embodiments 100 A, 100 B shown in FIGS. 1 A- 2 E , the linear actuators 117 A, 117 B comprise two parts: a base piece 117 A- 1 , 117 B- 1 and a moving piece 117 A- 2 , 117 B- 2 , respectively. The base pieces 117 A- 1 , 117 B- 1 are positioned in the their respective internal cavities 115 A, 115 B and is configured to be rotated about the longitudinal axis L but stationary so that they do not move in axial direction within the internal cavities 115 A, 115 B. The base pieces 117 A- 1 , 117 B- 1 and the moving pieces 117 A- 2 , 117 B- 2 threadedly engage each other to move the moving pieces 117 A- 2 , 117 B- 2 axially (i.e., up and down) within their respective internal cavities 115 A, 115 B. The one or more retractable members 130 A, 130 B are attached to their respective moving pieces 117 A- 2 , 117 B- 2 of the linear actuators 117 A, 117 B and by moving the moving pieces 117 A- 2 , 117 B- 2 axially, the retractable members 130 A, 130 B can be moved from their retracted position to being extended outward away from the stem component. Referring to the cross-sectional view in FIG. 1 G , in the prosthesis embodiment 100 A, the base piece 117 A- 1 comprises an internally threaded hole that is open toward the leading end 111 A and the threaded stem 117 A- 2 is received therein engaged by the mating threads. Because the base piece 117 A- 1 is stationary, turning the base piece 117 A- 1 clockwise or counter-clockwise will make the threaded stem 117 A- 2 to retract into away from the leading end 111 A or extend out of the base piece toward the leading end 111 A. This controlled up and down movement of the threaded stem 117 A- 2 can controllably move the one or more retractable members 130 A from the retracted position shown in FIGS. 1 A and 1 D outward and away from the longitudinal axis L to the fully extended position shown in FIGS. 1 C and 1 F , and any configuration in between. FIGS. 1 B, 1 E, and 1 G illustrate some of the intermediate positions. As previously mentioned, the one or more retractable members 130 A move through the opening 116 A provided in the generally cylindrical shell of the tibia stem component 110 A. Referring to FIG. 1 F , in this example embodiment, the proximal end 132 A of the one or more retractable members 130 A are connected to the threaded stem 117 A- 2 by a hinged connection H. The hinged connection H can be accomplished by a pin 117 A- 3 . The pin 117 A- 3 is shown in the exploded view of the prosthesis 100 A in FIG. 1 K . This hinged connection enables the threaded stem 117 A- 2 to move the one or more retractable members 130 A from their retracted position and extend them through the respective openings 116 A. Each of the one or more retractable members 130 A has a curved shape that facilitates the extending outward movement as the threaded stem 117 A- 2 pushes the proximal end 132 A of the retractable member 130 A upward. Referring to FIGS. 1 A and 1 D , as the proximal end 132 A of the retractable member 130 A is pushed up by the threaded stem 117 A- 2 , the top edge of the retractable member 130 A is urged against the top edge of the opening 116 A which guides the retractable member 130 A to extend outward as the retractable member 130 A swivels about the hinged joint H. The screw threads on the base piece 117 A- 1 and the threaded stem 117 A- 2 can be matched to be either left-handed or right-handed which will determine which direction the base piece 117 A- 1 needs to be turned to raise or lower the threaded stem 117 A- 2 . In the illustrated example, the base piece 117 A- 1 is configured to stay stationary in the axial direction while still being rotatable within the internal cavity 115 A by a pair of retaining pins RP. This can be better seen in FIGS. 1 H- 1 L . The base piece 117 A- 1 is configured with an annular groove 117 A- 1 G and the substantially cylindrical shell of the tibia stem component 110 A comprises two generally parallel through holes 111 A for receiving the retaining pins RP near the trailing end 112 A. The two through holes 111 A are positioned such that the retaining pins RP extend through the two through holes 111 A and are aligned with the annular groove 117 A- 1 G of the base piece 117 A- 1 so that the retaining pins RP intercept the groove from two opposing sides as shown in the cross-sectional views in FIGS. 1 H and 11 , and hold the base piece 117 A- 1 in place within the internal cavity 115 A. In some embodiments, the base piece 117 A- 1 is stationary near the trailing end 112 A within the internal cavity and the moving piece 117 A- 2 is movable along the longitudinal axis L of the tibia stem component with respect to the base piece by operation of the threaded engagement. The base piece 117 A- 1 can be provided with a tool-receiving socket 117 A- 1 S (See FIG. 1 G ) at the bottom end so that a tool such as a wrench or a screwdriver can be used to turn the base piece 117 A- 1 and control the movement of the one or more retractable members 130 A. Referring to the cross-sectional views in FIGS. 2 B- 2 D , in the prosthesis embodiment 100 B, the base piece 117 B- 1 comprises a threaded stem portion 117 B- 1 ′ and the moving piece 117 B- 2 is a threaded nut structure that threadedly engages the threaded stem portion 117 B- 1 ′. In other words, the threaded stem portion 117 B- 1 ′ is a leadscrew and the moving piece 117 B- 2 is the leadscrew nut that translates the rotational motion of the leadscrew into a linear motion. The proximal ends 132 B of the one or more retractable members 130 B are connected to the moving piece 117 B- 2 . Because the base piece 117 B- 1 is stationary, by turning the base piece 117 B- 1 clockwise or counter-clockwise, the moving piece 117 B- 2 can be moved up or down the threaded stem portion 117 B- 1 ′ by operation of their threaded engagement. This controlled up and down movement of the moving piece 117 B- 2 can controllably move the one or more retractable members 130 B from their retracted position shown in FIG. 2 C outward and away from the longitudinal axis L to their fully extended position shown in FIG. 2 D , and any configuration in between. As previously mentioned, the one or more retractable members 130 B move through the opening 116 B provided in the generally cylindrical shell of the tibia stem component 110 B. Referring to FIG. 2 D , in this example embodiment, the proximal end 132 B of the one or more retractable members 130 B are connected to the moving piece 117 B- 2 by a hinged connection H. The hinged connection H can be accomplished by connecting pins 117 B- 3 provided on the moving piece 117 B- 2 . The connecting pins 117 B- 3 are shown in the exploded view of the prosthesis 100 B in FIG. 2 E . This hinged connection enables the moving piece 117 B- 2 to move the one or more retractable members 130 B from their retracted position and extend them through the respective openings 116 B. Each of the one or more retractable members 130 B has a curved shape that facilitates the extending outward movement as the moving piece 117 B- 2 pushes the proximal end 132 B of the retractable member 130 B upward. Referring to FIGS. 2 C and 2 D , as the proximal end 132 B of the retractable member 130 B is pushed up by the moving piece 117 A- 2 , the top edge of the retractable member 130 B is urged against the top edge of the opening 116 B which guides the retractable member 130 B to extend outward as the retractable member 130 B swivels about the hinged joint H. The screw threads on the threaded stem portion 117 B- 1 ′ and the moving piece 117 B- 2 can be matched to be either left-handed or right-handed which will determine which direction the base piece 117 B- 1 needs to be turned to raise or lower the moving piece 117 B- 2 . The base piece 117 B- 1 can be provided with a tool-receiving socket (not shown) similar to the tool-receiving socket 117 A- 1 S of the base piece 117 A- 1 at the bottom end so that a tool such as a wrench or a screwdriver can be used to turn the base piece 117 B- 1 and control the movement of the one or more retractable members 130 B. In the illustrated example, the base piece 117 B- 1 is configured to stay stationary in the axial direction while still being rotatable within the internal cavity 115 B by a pair of retaining pins RP. The retaining pins RP works the same way as in the prosthesis 100 A. This can be better seen in the cross-sectional view in FIG. 2 B and the exploded views FIGS. 2 E- 2 F . The base piece 117 B- 1 is configured with an annular groove 117 B- 1 G and the substantially cylindrical shell of the tibia stem component 110 B comprises two generally parallel through holes 111 B for receiving the retaining pins RP near the trailing end 112 B. The two through holes 111 B are positioned such that the retaining pins RP extend through the two through holes 111 B and are aligned with the annular groove 117 B- 1 G of the base piece 117 B- 1 so that the pins RP intercept the groove from two opposing sides as shown in the cross-sectional views in FIGS. 1 H and 11 , and hold the base piece 117 B- 1 in place within the internal cavity 115 B. In some embodiments of the prosthesis 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, the proximal ends 132 C, . . . 132 H of the one or more retractable members 130 C, . . . 130 H are attached to the substantially cylindrical shell of the tibia stem 110 C, . . . 110 H and the distal end being a free end that engages the intramedullary canal's surrounding bone. In preferred embodiments, the one or more retractable members 130 C, . . . 130 H are hingeably attached to the substantially cylindrical shell of the tibia stem. In some embodiments of the prosthesis 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, the tibia stem 110 C, . . . 110 H further comprises a linear actuator 117 C, . . . 117 H provided within the internal cavity 115 C, . . . 115 H. The linear actuator 117 C, . . . 117 H is configured to be axially movable within the internal cavity along the longitudinal axis L. Each of the one or more retractable members 130 C, . . . 130 H have a distal end 131 C, . . . 131 H and a proximal end 132 C, . . . 132 H, and the proximal end is attached to the substantially cylindrical shell of the tibia stem 110 C, . . . 110 H. The distal end 131 C, . . . 131 H a free end that engages the intramedullary canal's surrounding bone. In preferred embodiments, the proximal end 132 C, . . . 132 H is hingeably attached to the substantially cylindrical shell of the tibial stem. In some embodiments of the prosthesis 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, the movement of the linear actuator 117 C, . . . 117 H toward the leading end 111 C, . . . 111 H of the tibia stem 110 C, . . . 110 H enables the one or more retractable members to move outward and away from the longitudinal axis L. In some embodiments, the linear actuator and the internal cavity's sidewall engage each other for moving the linear actuator within the internal cavity 115 C, . . . 115 H. In some embodiments, the linear actuator 117 C, . . . 117 H and the internal cavity's sidewall threadedly engage each other. For example, in the prosthesis embodiment 100 C shown in FIGS. 3 A- 3 J , the proximal end 132 C of each of the one or more retractable members 130 C comprises a cam surface 135 C (see FIGS. 31 and 3 J ) that is configured to engage the linear actuator 117 C. The linear actuator 117 C comprises a base piece 117 C- 1 and a top piece 117 C- 2 . As shown in the cross-sectional views shown in FIGS. 3 E, 3 F, 3 H, and 3 I , the top piece 117 C- 2 and the base piece 117 C- 1 are situated within the internal cavity 115 C with the top piece 117 C- 2 above the base piece 117 C- 1 . As shown in the exploded view in FIG. 3 J , the top piece and the base piece are assembled in such a way so that the base piece 117 C- 1 can be rotated about the longitudinal axis L relative to the top piece 117 C- 2 . In the illustrated example, the base piece 117 C- 1 comprises an axially located pin 117 C- 1 ′ that fits into a mating hole (not shown) provided on the top piece 117 C- 2 . In other embodiments, the location of the pin 117 C- 1 ′ can be reversed so that the top piece 117 C- 2 comprises the pin and the base piece 117 C- 1 comprises the mating hole. The base piece 117 C- 1 is threaded on its outer surface and the sidewall of the internal cavity 115 C is threaded so that the base piece 117 C- 1 and the tibia stem component 110 C threadedly engage each other. By turning the base piece 117 C- 1 clockwise or counter-clockwise, the base 117 C- 1 can be moved up or down within the internal cavity 115 C by operation of their threaded engagement. When the base piece 117 C- 1 moves up into the internal cavity 115 C, it pushes the top piece 117 C- 2 upward. As the top piece 117 C- 2 moves up, the leading end of the top piece 117 C- 2 is a cam engaging surface and contacts the cam surface 135 C of the one or more retractable members 130 C and moves the one or more retractable members 130 C from their retracted position shown in FIG. 3 C outward and away from the longitudinal axis L to their fully extended position shown in FIG. 3 H , and any configuration in between. As previously mentioned, the one or more retractable members 130 C move through the opening 116 C provided in the generally cylindrical shell of the tibia stem component 110 C. As used herein, the terms “cam surface” and “cam engaging surface” refer to any paired surfaces on two components, one on each component, that come in contact with each other and operate to result in urging one or both of the two components to move in an intended manner. Thus, one of the two paired surfaces is referred to as the cam surface and the corresponding surface on the other component is referred to as the cam engaging surface. The prosthesis 100 C comprises two pairs of retractable members 130 C. The retractable members 130 C in each pair are positioned opposite from each other, as shown in FIGS. 3 A, 3 D, and 3 G , and the leading end of the top piece 117 C- 2 extends between two retractable members 130 C in each pair. As shown in the cross-sectional views FIGS. 3 B, 3 C, 3 E, 3 F, 3 H, and 3 I , the leading end of the top piece 117 C- 2 is in contact with the cam surface 135 C of the retractable members 130 C. As shown in FIG. 3 J , the leading end of the top piece 117 C- 2 comprises two pairs of slanted surfaces 117 C- 2 ′ and 117 C- 2 ″ and each pair contacts the corresponding pairs of the cam surfaces 135 C of the retractable members 130 C. The movement of the retractable members 130 C from their retracted position outward and away from the longitudinal axis L is enabled by the engagement between the slanted surfaces 117 C- 2 ′ and 117 C- 2 ″ and the cam surfaces 135 C. As the linear actuator assembly 117 C is raised toward the leading end 111 C of the tibia stem component, the two pairs of the slanted surfaces 117 C- 2 ′ and 117 C- 2 ″ wedged between the two pairs of the cam surfaces contact the cam surfaces 135 C and pushes each of the retractable members to move from the retracted position outward and away from the longitudinal axis L. Referring to FIGS. 4 A- 4 G , in the prosthesis embodiment 100 D, the linear actuator 117 D comprises externally threaded surface 117 D′ (See FIG. 4 G ) that engages the corresponding threads on the sidewall of the internal cavity 115 D. By turning the linear actuator 117 D clockwise or counterclockwise, the linear actuator 117 D can be moved up or down within the internal cavity 115 D by operation of their threaded engagement. As the linear actuator 117 D moves up, the leading end of the linear actuator 117 D contacts the cam surface 135 D of the one or more retractable members 130 D and moves the one or more retractable members 130 D from their retracted position shown in FIG. 4 C outward and away from the longitudinal axis L toward the fully extended position shown in FIG. 4 F , and any configuration in between. The linear actuator 117 D can be provided with a tool-receiving socket 117 D-S(See FIGS. 4 D, 4 E, 4 F ) on the bottom end (the end near the trailing end 112 D) that is accessible through the opening 123 D at the trailing end 112 D so that a tool such as a wrench, a screwdriver, etc. can be used to turn the linear actuator 117 D. The one or more retractable members 130 D move through the opening 116 D provided in the generally cylindrical shell of the tibia stem component 110 D. Referring to FIGS. 5 A- 5 F , in the prosthesis embodiment 100 E, the linear actuator 117 E comprises externally threaded surface 117 E′ (See FIG. 5 E ) that engages the corresponding threads on the sidewall of the internal cavity 115 E. The linear actuator 117 E also can be provided with a tool-receiving socket similar to the socket 117 D-S on the bottom end that is accessible through the opening 123 E at the trailing end 112 E so that a tool such as a wrench, a screwdriver, etc. can be used to turn the linear actuator 117 E. Referring to FIGS. 7 A- 7 G , in the prosthesis embodiment 100 G, the linear actuator 117 G comprises a base piece 117 G- 1 and a top piece 117 G- 2 . This structure is similar to the two-piece configuration of the linear actuator 117 G described above. The base piece 117 G- 1 is threaded on its outer surface and the sidewall of the internal cavity 115 G is threaded so that the base piece 117 G- 1 and the tibia stem component 110 G threadedly engage each other. By turning the base piece 117 G- 1 clockwise or counterclockwise, the base 117 G- 1 can be moved up or down within the internal cavity 115 G by operation of their threaded engagement. When the base piece 117 G- 1 moves up into the internal cavity 115 G, it pushes the top piece 117 G- 2 upward. As the top piece 117 G- 2 moves up, the leading end of the top piece 117 G- 2 contacts the camming surface 135 G of the one or more retractable members 130 G and moves the one or more retractable members 130 G from their retracted position shown in FIG. 7 B outward and away from the longitudinal axis L to their fully extended position shown in FIG. 7 F , and any configuration in between. As previously mentioned, the one or more retractable members 130 G move through the opening 116 G provided in the generally cylindrical shell of the tibia stem component 110 G. In some embodiments of the prosthesis 100 C, 100 D, 100 E, 100 G, 100 H the linear actuator 117 C, 117 D, 117 E, 117 G, 117 H comprises a leading end and a trailing end corresponding with the direction of the tibia stem's leading end 111 C, 111 D, 111 E, 111 G, 111 H and trailing end 112 C, 112 D, 112 E, 112 G, 112 H, and the linear actuator further comprises a cam engaging surface 117 C- 2 ′ 117 D- 5 , 117 E- 5 , 117 G- 5 , 117 H- 5 near its leading end, and each of the proximal ends of the two or more retractable members comprises a cam surface 135 C, 135 D, 135 E, 135 G, 135 H that engages the cam engaging surface that enables the one or more retractable members to move outward and away from the longitudinal axis L when the linear actuator moves toward the leading end of the tibia stem. In some embodiments of the prosthesis, the distal surface 131 A, . . . 131 H of each of the one or more retractable members 130 A, . . . 130 H comprise a plurality of surface features that are configured to engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem within the intramedullary canal. Such surface features can be any surface feature such as surface texturing or teeth having a biased orientation. Referring to FIGS. 6 A- 6 G , according to some embodiments, disclosed is a prosthesis 100 F, wherein the tibia stem component 110 F further comprises an actuator 117 F provided within the internal cavity 115 F. The actuator 117 F is configured to be rotatable about the longitudinal axis L within the internal cavity. Each of the one or more retractable members 130 F have a distal end 131 F and a proximal end 132 F, the proximal end being attached to the tibia stem component 110 F and the distal end being a free end that engages the intramedullary canal's surrounding bone. The one or more retractable members 130 F are moved from the retracted position and extended outward and away from the longitudinal axis L by rotating the actuator 117 F within the internal cavity. In some embodiments of the prosthesis 100 F, the actuator 117 F comprises a leadscrew portion 117 F-S and the proximal end of each of the one or more retractable members comprises a toothed gear portion 136 F that is engaged with the leadscrew portion. Rotating the actuator 117 F engages the leadscrew 117 F-S and the toothed gear portion 136 F for moving the one or more retractable members from the retracted position. As shown in the cross-sectional views in FIGS. 6 B, 6 D, and 6 F , the actuator 117 F is positioned within the internal cavity 115 F aligned with the longitudinal axis L. The actuator 117 F comprises the leadscrew portion 117 F-S and a base portion 117 F-B. The base portion 117 F-B is provided with an annular groove 117 F-G for holding the actuator 117 F in the internal cavity 115 F while allowing it to rotate. This is achieved by a configuration similar to the way the base piece 117 A- 1 of the prosthesis embodiment 100 A is held within its internal cavity 115 A. The actuator 117 F is held in place by two retaining pins RP (see FIG. 6 G ) inserted through two substantially parallel through holes 113 F provided in the tibia stem component 110 F near the trailing end 112 F. The retaining pins RP engage the annular groove 117 F-G from substantially the opposite sides and hold the actuator 117 F in place while allowing the actuator 117 F to rotate about the longitudinal axis L. Referring to FIGS. 8 A- 8 G , in the prosthesis embodiment 100 H, the linear actuator 117 H comprises externally threaded surface 117 H′ (See FIG. 8 G ) that engages the corresponding threads on the sidewall of the internal cavity 115 H. By turning the linear actuator 117 H clockwise or counterclockwise, the linear actuator 117 H can be translated up or down within the internal cavity 115 H by operation of their threaded engagement. As the linear actuator 117 H moves up, the leading end of the linear actuator 117 H contacts the cam surface 135 H of the one or more retractable members 130 H and moves the one or more retractable members 130 H from their retracted position shown in FIG. 8 B outward and away from the longitudinal axis L toward the fully extended position shown in FIG. 8 E , and any configuration in between. The linear actuator 117 H also can be provided with a tool-receiving socket 117 H-S (See FIG. 8 G ) on the bottom end (the end near the trailing end 112 H) that is accessible through the opening 123 H (See FIG. 8 G ) at the trailing end 112 H so that a tool such as a wrench, a screwdriver, etc. can be used to turn the linear actuator 117 H. The one or more retractable members 130 H move through the opening 116 H provided in the generally cylindrical shell of the tibia stem component 110 H. In addition to the improved securement of the tibia stem component in the intramedullary canal, one additional beneficial feature of the prosthesis embodiments 100 A, 100 B, 100 E, 100 H is that the actuation direction of the one or more retractable members 130 A, 130 B, 130 E, and 130 H as they extend outward urges the tibia stem component further into the intramedullary canal. In this case, the tibial tray is drawn into the distal tibial cut surface at the ankle joint. In the embodiments of the prosthesis 100 E, 100 H, the distal ends 131 E, 131 H of the one or more retractable members 130 E, 130 H extend toward the leading end 111 E, 111 H of the tibia stem 110 E, 110 H when in the retracted position. Referring to FIGS. 9 A- 9 C , in the prosthesis embodiment 100 I, the tibia stem component 110 I comprises a linear actuator 117 I provided within the internal cavity 115 I. The linear actuator 117 I is configured to be movable within the internal cavity 115 I along the longitudinal axis L. The one or more retractable members 130 I are moved from the retracted position shown in FIG. 9 B and extended outward and away from the longitudinal axis L by translating the linear actuator 117 I within the internal cavity 115 I. In some embodiments, the linear actuator 117 I and the internal cavity's sidewall threadedly engage each other for translating the linear actuator 117 I within the internal cavity. A portion of the linear actuator 117 I is provided with male threads 117 I-T and the sidewall of the internal cavity 115 I is provided with corresponding female threads to achieve the threaded engagement. The bottom end of the linear actuator 117 I can be configured with a tool-receiving socket 117 I-S so that a tool such as a wrench or a screwdriver can be used to turn the linear actuator 117 I and control the movement of the one or more retractable members 130 I. In some embodiments of the prosthesis 100 I, translation of the linear actuator 117 I toward the leading end 111 I of the tibia stem component 110 I enables the one or more retractable members 130 I to extend outward. In some embodiments of the prosthesis 100 I, the linear actuator 117 I comprises a leading end and a trailing end corresponding with the direction of the tibia stem's leading end 111 I and trailing end 112 I, and further comprises a cam engaging surface 117 I-C near its leading end. Each of the one or more retractable members 130 I comprises a distal surface 131 I and a proximal surface 132 I with respect to the longitudinal axis L of the tibia stem component, wherein the proximal surface 132 I of each of the one or more retractable members 130 I is a cam surface that engages the cam engaging surface 117 I-C of the linear actuator. When the linear actuator 117 I is translated upward toward the leading end 111 I, the cam engaging surface 117 I-C pushes against the cam surface 132 I (i.e. the proximal surface) and enables the one or more retractable members 130 I to be pushed from their retracted position shown in FIGS. 9 A- 9 B outward and away from the longitudinal axis L toward the fully extended position shown in FIG. 9 C , and any configuration in between. In some embodiments of the prosthesis 100 I, the distal surface 131 I of each of the one or more retractable members 130 I comprises a plurality of surface features that are configured to engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem component 110 I within the intramedullary canal. In the illustrated example shown in FIGS. 9 A- 9 B , the plurality of surface features on the distal surface 131 I are teeth having a biased orientation. Referring to FIGS. 9 D- 9 F , in the prosthesis embodiment 100 J, the tibia stem component 110 J comprises a linear actuator 117 J provided within the internal cavity 115 J. The linear actuator 117 J is configured to be movable within the internal cavity 115 J along the longitudinal axis L. Two or more retractable members 130 I provided in the tibia stem component 110 J are moved from the retracted position shown in FIG. 9 B and extended outward and away from the longitudinal axis L by translating the linear actuator 117 J within the internal cavity 115 J. In some embodiments, the linear actuator 117 J and the internal cavity's sidewall threadedly engage each other for translating the linear actuator 117 J within the internal cavity. A portion of the linear actuator 117 J is provided with male threads 117 J-T and the sidewall of the internal cavity 115 J is provided with corresponding female threads to achieve the threaded engagement. The bottom end of the linear actuator 117 J can be configured with a tool-receiving socket 117 J-S so that a tool such as a wrench or a screwdriver can be used to turn the linear actuator 117 J and control the movement of the two or more retractable members 130 J. In some embodiments of the prosthesis 100 J, translation of the linear actuator 117 J toward the leading end 111 J of the tibia stem component 110 J enables the two or more retractable members 130 J to extend outward. In some embodiments of the prosthesis 100 J, the linear actuator 117 J comprises a leading end and a trailing end corresponding with the direction of the tibia stem's leading end 111 J and trailing end 112 J, and further comprises a cam engaging surface 117 J-C near its leading end. Each of the two or more retractable members 130 J comprises a distal surface 131 J and a proximal surface 132 J with respect to the longitudinal axis L of the tibia stem component, wherein the proximal surface 132 J of each of the two or more retractable members 130 J is a cam surface that engages the cam engaging surface 117 J-C of the linear actuator. When the linear actuator 117 J is translated upward toward the leading end 111 J, the cam engaging surface 117 J-C pushes against the cam surface 132 J (i.e. the proximal surface) and enables the two or more retractable members 130 J to be pushed from their retracted position shown in FIG. 9 D outward and away from the longitudinal axis L toward the fully extended position shown in FIG. 9 E , and any configuration in between. In some embodiments of the prosthesis 100 J, the distal surface 131 J of each of the two or more retractable members 130 J comprises a plurality of surface features that are configured to engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem component 110 J within the intramedullary canal. In the illustrated example shown in FIGS. 9 D- 9 F , the plurality of surface features on the distal surface 131 J are teeth having a biased orientation. Each distal surface 131 J has two teeth as shown. The two or more retractable members 130 J are held together by an elastic ring 30 J, such as a rubber band. (See FIGS. 9 E- 9 F ). Each of the two or more retractable members 130 J are configured with a groove 130 J-G (See FIG. 9 F ) for receiving the elastic ring 30 J. The elastic ring 30 J pulls the two or more retractable members 130 J toward the axial center of the tibia stem component 110 J and keep the retractable members 130 J, particularly the cam surface 132 J of the retractable members 130 J, in contact with the cam engaging surface 117 J-C. In some embodiments of the prosthesis, the prosthesis can be structured similar to the embodiments 100 C, 100 D, 100 E, 100 F, 100 G, 100 H, except that rather than having the linear actuators 117 C, 117 D, 117 E, 117 G, and 117 H that engage the one or more retractable members, an actuator (not shown) such as a rod or a stick can be inserted into the internal cavity 115 C, . . . 115 H via the opening 123 C, . . . 123 H at the trailing end 112 C, . . . 112 H of the tibia stem to engage and move the one or more retractable members. In such embodiments, the leading tips of the actuator would be configured similar to the linear actuators 117 C, 117 D, 117 E, 117 G, and 117 H to appropriately engage the cam surfaces 135 C, 135 D, 135 E, 135 G, and 135 H of the one or more retractable members. Referring to FIGS. 10 A- 10 F , ankle prostheses 200 A, 300 A according to other embodiments of the present disclosure are disclosed. The prosthesis 200 A, 300 A comprises: a tibia stem component 210 A, 310 A and a tibia tray component 220 A, 320 A. The tibial stem component 210 A, 310 A comprises a leading end 211 A, 311 A, a trailing end 212 A, 312 A and a longitudinal axis L defined therethrough. The tibia tray component 220 A, 320 A is generally configured to be attached to a prosthetic joint articulating surface. The tibia tray component 220 A, 320 A extends from the trailing end 212 A, 312 A of the tibia stem component 210 A, 310 A. The tibia stem component 210 A, 310 A is sized and configured to be disposed in an intramedullary canal formed in a tibia. The tibia stem component 210 A, 310 A is divided into two or more retractable members 230 A, 330 A by longitudinal slits 231 A, 331 A formed in the tibia stem. The longitudinal slits 231 A, 331 A extend from the leading end 211 A, 311 A of the tibia stem component and partially toward the trailing end 212 A, 312 A, thereby defining each of the two or more retractable members 230 A, 330 A between a pair of the longitudinal slits 231 A, 331 A. The two or more retractable members 230 A, 330 A have proximal ends that are joined near the trailing end 212 A, 312 A of the tibia stem component and distal ends 233 A, 333 A that are freely moveable at the leading end 211 A, 311 A. The two or more retractable members 230 A, 330 A are configured to be controllably movable from a retracted position (shown in FIGS. 10 A, 10 B, and 10 D ) and have their free distal ends 233 A, 333 A at the leading end 211 A, 311 A be bent outward and away from the longitudinal axis L. In their retracted position, the two or more retractable members 230 A, 330 A are parallel to the longitudinal axis L and do not extend outward. When the tibia stem component 210 A, 310 A is disposed in the intramedullary canal and the two or more retractable members 230 A, 330 A are moved outward away from the longitudinal axis L, the two or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem component 210 A, 310 A within the intramedullary canal. Referring to FIGS. 10 B- 10 F , the two or more retractable members 230 A, 330 A define an internal cavity 215 A, 315 A that is open at both the leading end 211 A, 311 A of the tibia stem and the trailing end 212 A, 312 A of the tibia stem. The opening 213 A, 313 A at the trailing end 212 A, 312 A is accessible from the bottom side of the tibial tray 220 A, 320 A as shown in FIGS. 10 B and 10 F . The tibia stem 210 A, 310 A further comprises a linear actuator 217 A, 317 A provided within the internal cavity 215 A, 315 A. The linear actuator 217 A, 317 A is configured to be movable within the internal cavity 215 A, 315 A along the longitudinal axis L, whereby the two or more retractable members 230 A, 330 A are moved from the retracted position and extend outward by moving the linear actuator 217 A, 317 A within the internal cavity 215 A, 315 A. In some embodiments, the linear actuator 217 A, 317 A and the internal cavity's sidewall threadedly engage each other for moving the linear actuator 217 A, 317 A within the internal cavity 215 A, 315 A. The translation of the linear actuator 217 A, 317 A toward the trailing end 212 A, 312 A of the tibia stem component enables the two or more retractable members 230 A, 330 A, specifically the distal ends 233 A, 333 A, to extend outward away from the longitudinal axis L. In some embodiments, the linear actuator 217 A, 317 A comprises a leading end and a trailing end corresponding with the direction of the tibia stem's leading end 211 A, 311 A and trailing end 212 A, 312 A, and further comprises a cam surface 217 A- 2 , 317 A- 2 near its leading end. The side of each of the one or more retractable members 230 A, 330 A facing the internal cavity 215 A, 315 A engage the cam surface of the linear actuator 217 A, 317 A and will be referred to herein as the “cam engaging surface” 235 A, 335 A. (See FIG. 10 B, 10 G ). The cam surface 217 A- 2 , 317 A- 2 and the cam engaging surface 235 A, 335 A are configured to push the two or more retractable members 230 A, 330 A outward and away from longitudinal axis L when the linear actuator 217 A, 317 A translates toward the trailing end 212 A, 312 A of the tibia stem component. As can be seen in FIGS. 10 B and 10 C , the cam surface 217 A- 2 , 317 A- 2 portion of the linear actuator 217 A, 317 A has an inverse frusto-conical shape so that the diameter of the distal tip of the cam surface portion is greater than the diameter of the internal cavity 215 A, 315 A formed by the cam engaging surfaces 235 A, 335 A of the two or more retractable members 230 A, 330 A. Thus, as the linear actuator 217 A, 317 A is translated downward in the orientation shown in FIG. 10 B, 10 G toward the trailing end 212 A, 312 A of the tibia stem component 210 A, 320 A, the cam surface portion 217 A- 2 , 317 A- 2 pushes the two or more retractable members 230 A, 330 A outward away from the longitudinal axis L, effectively making the outside diameter of the leading end 211 A, 311 A of the tibia stem component larger. The distal tip 233 A, 333 A of the two or more retractable members 230 A, 330 A will move further outward as the linear actuator 217 A, 317 A is translated further toward the trailing end 212 A, 312 A. Thus, this controlled outward movement of the two or more retractable members 230 A, 330 A can be used to control the amount of force the two or more retractable members 230 A, 330 A are applying against the surrounding bone inside the intramedullary canal to secure the prosthesis inside the intramedullary canal. In the tibia stem embodiment 200 A, the linear actuator 217 A comprises a threaded portion 217 A- 1 on its outer surface (see FIG. 10 C ) and the sidewall of the internal cavity 215 A comprises a threaded portion 213 A- 1 (see FIG. 10 B ). Engagement of these screw threaded surfaces enables translation of the linear actuator 217 A. By turning the linear actuator 217 A clockwise or counter-clockwise, the linear actuator 217 A can be moved up or down within the internal cavity 215 A by operation of their threaded engagement. The linear actuator 217 A can be provided with a tool-receiving socket 217 A-S on the bottom end (the end near the trailing end 212 A) that is accessible through the opening 213 A (See FIG. 10 B ) at the bottom of the tibial tray portion 220 A so that a tool such as a wrench, a screwdriver, etc. can be used to turn the linear actuator 217 A. Referring to FIGS. 10 F- 10 H , in the tibia stem embodiment 300 A, the linear actuator 317 A is configured with a threaded hole 317 A- 1 open to its bottom end for receiving a threaded bolt 318 A. The threaded bolt 318 A is inserted into the threaded hole 317 A- 1 via a hole 313 A at the bottom of the tibial tray portion 320 A. Engagement of these screw threaded surfaces enables translation of the linear actuator 317 A. By turning the threaded bolt 318 A clockwise or counter-clockwise, the linear actuator 317 A can be moved up or down by operation of their threaded engagement. The linear actuator 317 A can be provided with a tool-receiving socket 317 A-S on the bottom end that is accessible through the opening 313 A (See FIG. 10 G ) at the bottom of the tibial tray portion 320 A so that a tool such as a wrench, a screwdriver, etc. can be used to turn the threaded bolt 318 A. Preferably, to prevent the linear actuator 317 A from turning when the threaded bolt 318 A is being threaded into the linear actuator 317 A, the linear actuator 317 A can be provided with one or more boss 317 A- 3 that protrudes from the exterior of the linear actuator 317 A. Each of the one or more boss 317 A- 3 extends between two retractable members 330 A and prevents the linear actuator 317 A from rotating about its longitudinal axis when the threaded bolt 318 A is being turned. In other words, the one or more boss 317 A- 3 provides counter-torque to the linear actuator 317 A. The boss 317 A- 3 can take a variety of shapes such as one or more ridges, splines, edges, grooves, etc. that meshes with the two or more retractable members 330 A. In some embodiments, the two or more retractable members 230 A, 330 A can comprise a plurality of surface features 237 A that are configured to enhance the engagement with the intramedullary canal's surrounding bone and enhance anchoring the tibia stem component 210 A, 310 A within the intramedullary canal when the tibia stem component is disposed in the intramedullary canal and the two or more retractable members 230 A, 330 A are moved outward to engage the surrounding bone. In some embodiments, the surface features 237 A can be surface texturing or teeth having a biased orientation. For example, in the illustrated embodiment shown in FIGS. 10 A- 10 C , the outer surface of the two or more retractable members 230 A are provided with a plurality of teeth having a biased orientation that will resist the tibia stem component from being pulled out of the intramedullary canal. once the two or more retractable members 230 A are deployed outward and the plurality of surface features 237 A engage the surrounding bone in the intramedullary canal. Referring to FIGS. 11 A- 11 F , according to other embodiments of the present disclosure, disclosed is an ankle prosthesis 200 B comprising: a tibia stem component 210 B and a tibia tray component 220 B. The tibial stem component 210 B comprises a leading end 211 B, a trailing end 212 B, and a longitudinal axis L defined therethrough. The tibia tray component 220 B is generally configured to be attached to a prosthetic joint articulating surface. The tibia tray component 220 B extends from the trailing end 212 B of the tibia stem component 210 B. The tibia stem component 210 B is sized and configured to be disposed in an intramedullary canal formed in a tibia. The tibia stem component 210 B is divided into two or more retractable members 230 B by longitudinal slits 231 B (see FIGS. 11 A, 11 F ) formed in the tibia stem component 210 B. The longitudinal slits 231 B extend from the leading end 211 B of the tibia stem component and partially toward the trailing end 212 B, thereby defining each of the two or more retractable members 230 B between a pair of the longitudinal slits 231 B. The two or more retractable members 230 B have proximal ends that are joined near the trailing end 212 B of the tibia stem component and distal ends 233 B (see FIGS. 11 D, 11 F ) that are freely moveable at the leading end 211 B. The two or more retractable members 230 B are configured to be controllably movable from a retracted position (shown in FIGS. 11 A and 11 B ) to an extended position in which their free distal ends 233 B at the leading end 211 B be bent outward and away from the longitudinal axis L. In their retracted position, the two or more retractable members 230 B are parallel to the longitudinal axis L and do not extend outward. When the tibia stem component 210 B is disposed in the intramedullary canal and the two or more retractable members 230 B are moved outward away from the longitudinal axis L, the two or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem component 210 B within the intramedullary canal. The two or more retractable members 230 B define an internal cavity 215 B that is open at both the leading end 211 B of the tibia stem component and the trailing end 212 B of the tibia stem. The internal cavity 215 B can be best seen in FIG. 11 F . The tibia stem component 210 B further comprises a linear actuator 217 B provided within the internal cavity 215 B. The linear actuator 217 B is configured to be movable within the internal cavity 215 B along the longitudinal axis L, whereby the two or more retractable members 230 B are moved from the retracted position and extend outward by moving the linear actuator 217 B within the internal cavity 215 B. Referring to FIGS. 11 D- 11 E , similar to the linear actuator 217 A in the prosthesis 200 A, the linear actuator 217 B comprises a first portion 217 B- 1 that has a larger diameter than the remaining second portion 217 B- 2 and a transition portion in between that forms a cam surface 217 B-C. The linear actuator 217 B is situated inside the internal cavity 215 B so that the first portion 217 B- 1 is at the leading end 211 B (see FIG. 11 B for the notation) of the tibia stem component. The interior sides of the two or more retractable members 230 B that are facing into the internal cavity 215 B are configured so that when the linear actuator 217 B is translated downward toward the trailing end 216 B of the tibia stem component 210 B, the large diameter first portion 217 B- 1 interacts with the two or more retractable members 230 B to push them outward and away from the longitudinal axis L. In some embodiments, the contour of the interior sides of the two or more retractable members 230 B are configured so that the diameter of the internal cavity 215 B matches the reducing diameter of the linear actuator 217 B going from the leading end 211 B to the trailing end 212 B. Thus, the interior surface of each of the two or more retractable members 230 B comprise a cam engaging surface 230 B-C that correspond to the cam surface 217 B-C. This configuration is illustrated in FIGS. 11 D- 11 E . Then, starting from the retracted configuration for the two or more retractable members 230 B shown in FIGS. 11 D- 11 E , when the linear actuator 217 B is translated downward toward the trailing end 212 B, the cam surface 217 B-C and the cam engaging surface 230 B-C operate on one another to push the two or more retractable members 230 B outward and away from the longitudinal axis L. The distal tip 233 B of the two or more retractable members 230 B will move further outward as the linear actuator 217 B is translated further toward the trailing end 212 B. Thus, this controlled outward movement of the two or more retractable members 230 B can be used to control the amount of force the two or more retractable members 230 B are applying against the surrounding bone inside the intramedullary canal to secure the prosthesis inside the intramedullary canal. Referring to FIGS. 11 A- 11 E , because the lower portion (i.e., closer to the trailing end 212 B) of the two or more retractable members 230 B becomes thicker as the diameter of the internal cavity 215 B becomes smaller, this increase in thickness can hinder the ability for the retractable members 230 B to flex or bend outward. This can be especially true if the two or more retractable members 230 B are made of stiff material. Therefore, in some embodiments, each of the two or more retractable members 230 B can be provided with one or more thinner necked regions 230 B-N to tune the flexibility of the retractable members 230 B to achieve either plastic or elastic deformation that would be suitable to the material, size, and anatomical application. Such necked regions 230 B-N can be created by cutouts on the exterior and/or interior sides of the retractable members 230 B. The translation of the linear actuator 217 B is achieved by the use of a base nut 225 B. (See FIGS. 11 D, 11 E, and 11 F ). The tibia tray component 220 B in this embodiment comprises a hole 223 B that aligns with the internal cavity 215 B so that the threaded portion 217 B-S of the linear actuator 217 B can be extended downward and through the hole 223 B. The base nut 225 B is threaded onto the threaded portion 217 B-S from the bottom side of the tibia tray component 220 B. Surrounding the hole 223 B is a flange 224 B (See FIG. 11 F ) and by tightening the base nut 225 B the flange 224 B is captured between the base nut 225 B and the tibia stem component 210 B. Thus, with the base nut 225 B braced against the flange 224 B, turning the base nut 225 B and engaging the threaded portion 217 B-S will pull the linear actuator 217 B downward toward the trailing end 211 B. This downward motion causes the stem component 210 b to expand circumferentially, applying a hoop-like stress to the surrounding bone and embedding the implant. In one embodiment, the retractable members 230 B are configured and arranged to bend within their elastic deformation range for the implant material of choice. Keeping the design within the elastic deformation range allows the retractable members 230 B to spring back to the original position and allow for easy implant removal out of bone forming the intramedullary canal. Polyaxial Feature According to some embodiments, the tibial stem component and the tibial tray component of the ankle prosthesis can be configured to be modular pieces so that the angle between the two components can be adjusted to be within a range of angles rather than being fixed to one configuration. Some examples of such ankle prosthesis are disclosed with the accompanying illustrations in FIGS. 11 A- 121 . In some embodiments, the ankle prosthesis 200 B, 300 B comprises a tibia stem component 210 B, 310 B and a tibia tray component 220 B, 320 B. The tibia stem component comprises a leading end 211 B, 311 B, a trailing end 212 B, 312 B, and a longitudinal axis L defined therethrough. The tibia tray component 220 B, 320 B comprises a surface 220 B-S, 320 B-S defining a reference plane REF (see FIG. 11 E, 12 F, 12 G ). The tibia stem component and the tibia tray component are modular and the tibia tray component 220 B, 320 B and the trailing end of the tibia stem component 210 B, 310 B are configured to form a joint wherein the tibia stem component's relative angle with respect to the reference plane REF can be adjusted so that the longitudinal axis L of the tibia stem component 210 B, 310 B forms an angle θ (see FIG. 11 E ) with an orthogonal OL of the reference plane REF, wherein the angle θ can be between 0 degrees up to and including 45 degrees. In one embodiment, the angle θ can range between 0 degrees up to and including 40 degrees. In one embodiment, the angle θ can range between 0 degrees up to and including 30 degrees. In one embodiment, the preferred angle θ can range between 0 degrees up to and including 20 degrees. In other joints of the body, this angular adjustability may be adjusted between 0 and 90 degrees, and as is suitable to the anatomy. The angular range is configured and arranged to suit the implant's size as well as anatomical considerations. In one embodiment, not shown, the angular range may be limited by flat faces in the apparatus's ball joint which limit angular motion in one plane differently than in another plane. This includes a uni-planar adjustable design which may allow for more angular adjustment in the anterior-posterior direction (sagittal plane) while limiting angular motion in medial lateral direction (coronal). The tibia stem component 210 B, 310 B is sized and configured to be disposed in an intramedullary canal formed in a tibia. The tibia stem component comprises: two or more retractable members 230 B, 330 B, configured to be controllably movable from a retracted position and be extended outward and away from the longitudinal axis L. In the retracted position, the two or more retractable members 230 B, 330 B are contained substantially within the silhouette of the tibia stem component and do not extend outward. When the tibia stem component is disposed in the intramedullary canal and the one or more retractable members 230 B, 330 B are extended outward, the one or more retractable members engage the intramedullary canal's surrounding bone and enhance anchoring the tibia stem within the intramedullary canal. The adjustable joint formed between the tibial stem component 210 B, 310 B and the tibial tray component 220 B, 320 B can be secured to fix the angle θ at a desired angle between the above-mentioned range between 0 degrees up to and including 45 degrees. The tibia tray component 220 B, 320 B is configured with a recess 224 B, 324 B on the top surface 220 B-S, 320 B-S of the tibia tray component 220 B, 320 B for receiving the trailing end 212 B, 312 B of the tibia stem component 210 B, 310 B. The bottom of the recess 224 B, 324 B is configured with a convex surface to receive the trailing end 212 B, 312 B of the tibial stem component 210 B, 310 B and allow the tibia stem component 210 B, 310 B to swivel against the convex surface to adjust the angle θ to a desired angle. Once the desired angle θ is achieved, the position of the tibia stem component 210 B, 310 B can be locked by threading the locking nut 225 B, 325 B onto the threaded portion 217 B-S, 317 B-S of the linear actuator 217 B, 317 B. The locking nut 225 B, 325 B captures the flange 224 B, 324 B between the locking nut 225 B, 325 B and the tibia stem component 210 B, 310 B and tightening the locking nut 225 B, 325 B locks the assembly's configuration. In some embodiments, supplemental locking features can be used in conjunction with the locking nut 225 B, 325 B to enhance the locking function. Such supplemental locking features can be in the form of nylon washers, locking washers, distorted thread nuts, serrated face nuts, or other locking nut/washer combinations. In some embodiments, Spiralock® thread forms by Stanley® Engineering Fastening can be used. This polyaxial adjustment feature allows the prosthesis to be adjusted to the variations in the patients' physiology during the ankle prosthesis implantation surgical procedure. Some Material Considerations In some embodiments, the tibia stem components 210 A, 310 A, and 210 B of the prostheses 200 A, 310 A, and 200 B, respectively, can be made of a memory metal alloys such as Nitinol so that the superelastic properties or the memory properties of such alloy can be employed to enhance the function of the two or more retractable members 230 A, 330 A, and 230 B. The polyaxial adjustment feature can also be applied on tibia stem prostheses that comprise stackable modular tibia stem components, for example, the tibia stem components in Wright Medical's Inbone™ Total Ankle System. An example of such tibia stem prosthesis 400 is illustrated in FIGS. 13 A- 13 B . In some embodiments, the ankle prosthesis 400 comprises a tibia stem component 430 and a tibia tray component 420 . The tibia stem component can comprise two or more modular stem pieces that are configured to be stacked and securely engage to each other. The two or more modular stem pieces can include a base stem component 430 B, a top stem component 430 T, and one or more middle stem component 430 M. The modular stem pieces can be threaded into each other. The modular configuration of the tibia stem 430 allows the surgeon to configure different lengths for the tibia stem based on the condition and dimension of the patient's tibia. The diameter of the modular stem pieces can be varied also. In the illustrated example, the tibia stem component 430 includes three modular pieces: the base stem component 430 B, the middle stem component 430 M, and the top stem component 430 T. The base stem component 430 B is configured to form a joint wherein the base stem component's relative angle with respect to the reference plane REF can be adjusted so that the longitudinal axis L of the base stem component 430 B forms an angle θ (see FIG. 13 B ) with an orthogonal OL of the reference plane REF, wherein the angle θ can be between 0 degrees up to and including 45 degrees. In the configuration illustrated in FIG. 13 B , the angle θ is 0. The reference plane REF is defined by a surface 420 -S that is on the proximal side (in the orientation of the tibia tray 420 as installed on to the prepared distal end of the patient's tibia) of the tibia tray component 420 . In one embodiment, the angle θ can range between 0 degrees up to and including 40 degrees. In one embodiment, the angle θ can range between 0 degrees up to and including 30 degrees. In one embodiment, the preferred angle θ can range between 0 degrees up to and including 20 degrees. In other joints of the body, this angular adjustability may be adjusted between 0 and 90 degrees, and as is suitable to the anatomy. The angular range is configured and arranged to suit the implant's size as well as anatomical considerations. In one embodiment, not shown, the angular range may be limited by flat faces in the apparatus's ball joint which limit angular motion in one plane differently than in another plane. This includes a uni-planar adjustable design which may allow for more angular adjustment in the anterior-posterior direction (sagittal plane) while limiting angular motion in medial lateral direction (coronal). The adjustable joint formed between the base stem component 430 B and the tibia tray component 420 can be secured to fix the angle θ at a desired angle between the above-mentioned range between 0 degrees up to and including 45 degrees. The tibia tray component 420 is configured with a recess 424 on the top surface 420 -S of the tibia tray component 420 for receiving a trailing end 432 B of the base stem component 430 B. The bottom of the recess 424 is configured with a convex surface to receive the trailing end 432 B of the base stem component 430 B and allow the assembled tibia stem component 430 to swivel against the convex surface to adjust the angle θ to a desired angle. The convex surface at the bottom of the recess 424 is convex in the proximal direction. Once the desired angle θ is achieved, the position of the tibia stem component 430 can be locked by threading a locking bolt 425 into the base stem component 430 B from the distal side of the tibia tray 420 through a hole 423 that is provided in the convex surface of the recess 424 . The convex surface forms an annular flange 424 F around the hole 423 . The locking bolt 425 comprises a head portion and a threaded shaft portion 418 . The threaded shaft portion 418 has a male-type threads and the base stem component 430 B is configured with a corresponding female type threaded hole 438 B for receiving the threaded shaft portion 418 . As shown in the longitudinal cross-sectional view in FIG. 13 B , the head portion of the locking bolt 425 is larger than the diameter of the hole 423 and captures the flange 424 F between the head portion of the locking bolt 425 and the base stem component 430 B and tightening the locking bolt 425 locks the assembly's configuration. The locking bolt 425 threadedly engages the trailing end of the tibial stem component 430 from the distal surface of the tibia tray to lock the joint at the angle θ. In some embodiments, supplemental locking features can be used in conjunction with the locking bolt 425 to enhance the locking function. Such supplemental locking features can be in the form of nylon washers, locking washers, distorted thread nuts, serrated face nuts, or other locking nut/washer combinations. In some embodiments, Spiralock® thread forms by Stanley® Engineering Fastening can be used. The tibia stem component and/or the tibia tray component in the various embodiments of the prosthesis disclosed herein can be made of any total joint material of materials commonly used in the prosthetic art, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel, polyethylene, absorbable polymer, or any other total joint replacement metal and/or ceramic. In some embodiments, the tibia stem component and/or the tibia tray component can comprise a coating of 3 D printed Biofoam™, Adaptis™ porous metal, sintered glass, artificial bone, any uncemented metal or ceramic surface, or a combination thereof that would promote bony in-growth. The tibia stem component and/or the tibia tray component can further be covered with one or more coatings such as antimicrobial, antithrombotic, and osteoinductive agents, or a combination thereof. In embodiments where the above-mentioned porous coating is provided, these agents can further be carried in a biodegradable carrier material with which the pores in the porous coating can be impregnated. Although the examples of the inventive structures illustrated herein are exemplified as tibia stem and tray components of an ankle replacement prosthesis, the inventive structures are equally applicable in other physical joints in human or animal skeleton. It will be understood that the foregoing description is of exemplary embodiments of this invention, and that the invention is not limited to the specific forms shown. Modifications may be made in the design and arrangement of the elements without departing from the scope of the invention.